The present invention relates to an apparatus for washing semiconductor wafers subjected to chemical treatment in the process of fabrication of semiconductor devices.
A cascade-type washing apparatus has been conventionally used for washing semiconductor wafers. This type of apparatus includes a plurality of washing tubs arranged in a cascade, and chemically inert water, namely pure water distilled or treated by ion-exchange, is constantly supplied to the uppermost tub of the apparatus. The pure water that overflows from the uppermost tub is carried down into the succeeding tubs one after another and ultimately into the lowermost tub. With the water run, a basket holding semiconductor wafers is placed first in the lowermost tub and is then transferred to the upper tubs in sequence, and thus the wafers are washed. This type of washing apparatus, however, has many defects in that part of the chemical waste removed from the wafers remains undrained with a certain amount of water stagnating in the tubs, with the result that the wafers are again contaminated by the residue of the waste near the water surface each time they leave the tub. Furthermore, the water flow along the wafers is as slow as several tens of centimeters per second, where substantial washing efficiency can hardly be expected. Stil further, because the wafers are held in parallel in the basket with their edges retained in grooves formed inside the basket, the retained part of the wafer surfaces cannot be washed thoroughly. Further, in the type of apparatus in which the washing water is periodically replaced, the water level recedes along the wafer surfaces, and residual chemical waste and solid particles floating on the surface of the water contaminate the wafers.
It is therefore an object of the present invention to provide a washing apparatus capable of thoroughly washing semiconductor wafers without allowing contaminants to be adhered again to the wafer surfaces.
It is another object of the invention to provide a washing apparatus capable of washing semiconductor wafers in a reduced period of time and with a minimum amount of washing liquid.
A washing apparatus for semiconductor wafers according to the present invention comprises a single washing tub in which semiconductor wafers are placed, means for constantly squirting a washing liquid downward to the wafers, means for constantly squirting a washing liquid upward to the wafers, and means for periodically draining the waste liquid from a position below the wafers.